Final Phase is just tartaric acid, citric acid and malic acid.
FloraKleen is citric acid, dextrose and sucrose (this is what people say, there's no true analysis on it.. anywhere.. kind of strange.. even the MSDS lists the ingredients as a "trade secret")
I'd say this makes the Final Phase better as the acids are available in different forms and they all absorb and purge the metals at different rates.
I picked up a bottle of locally sourced "Flush" today actually, the ingredients? Citric Acid, Tataric Acid and Malic Acid..
What are these things? Well.. lemon and lime juice really.

All three of them are found in sour/citrus fruits...
I've considered watering my plant with grapefruit juice and water for the last two weeks, what do you think'll happen? Maybe throw some Gin in too?
Read this if you have time..
http://www.bioline.org.br/pdf?st10048
These flushes do work, they're not just "sugar water" as most naysayers like to believe.. they do serve a purpose and have research to prove it but should not be used up until the day of harvest, IMO.
Flush w/ solution then switch to plain water for 2 waterings.. or if you get within 2 weeks of harvest and your leaves are still as green as a fresh Christmas tree, flush w/ solution twice, then switch to plain water for 2 waterings..
ECE is on point though, same amount of time used in flushing as you would for a photo.. you're flushing the medium and forcing the plant to use up stored reserves.. that's the goal.